hfsplus: get rid of write_super

This patch makes hfsplus stop using the VFS '->write_super()' method along with
the 's_dirt' superblock flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblocks using the '->write_super()' call-back.  But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Tested using fsstress from the LTP project.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/hfsplus/inode.c b/fs/hfsplus/inode.c
index 7009265..3d8b4a6 100644
--- a/fs/hfsplus/inode.c
+++ b/fs/hfsplus/inode.c
@@ -431,7 +431,7 @@
 		sbi->file_count++;
 	insert_inode_hash(inode);
 	mark_inode_dirty(inode);
-	sb->s_dirt = 1;
+	hfsplus_mark_mdb_dirty(sb);
 
 	return inode;
 }
@@ -442,7 +442,7 @@
 
 	if (S_ISDIR(inode->i_mode)) {
 		HFSPLUS_SB(sb)->folder_count--;
-		sb->s_dirt = 1;
+		hfsplus_mark_mdb_dirty(sb);
 		return;
 	}
 	HFSPLUS_SB(sb)->file_count--;
@@ -455,7 +455,7 @@
 		inode->i_size = 0;
 		hfsplus_file_truncate(inode);
 	}
-	sb->s_dirt = 1;
+	hfsplus_mark_mdb_dirty(sb);
 }
 
 void hfsplus_inode_read_fork(struct inode *inode, struct hfsplus_fork_raw *fork)